Plan 9 from Bell Labs’s /n/sources/contrib/nemo/sys/lib/plumb/fileaddr
addrelem='((#?[0-9]+)|(/[A-Za-z0-9_\^]+/?)|[.$])' addr=:($addrelem([,;+\-]$addrelem)*) url='(https?|ftp|file|gopher|mailto|news|nntp|telnet|wais|prospero)://[a-zA-Z0-9_@\-]+([.:][a-zA-Z0-9_@\-]+)*/?[a-zA-Z0-9@_?,%#~&/\-+=]+([:.][a-zA-Z0-9_?,@%#~&/\-+=]+)*'
(This is a user-contributed directory and should not be interpreted as statement by Alcatel-Lucent.)